How to round 431801 to four sig figs?

431800... all numbers that aren't 0 are significant... unless the zeros come at the end after a decimal point such as 4.900 (4 sig figs), or they are sandwiched between other significant numbers such as 201 (3 sig figs) then they are significant. also if there is a decimal put nothing after it, everything in front is a sig fig such as 40. (2 sig figs) because it is exactly 40